Demonstrators calling for an increase in the minimum wage to $15-dollars-per-hour march to McDonald's headquarters during a protest in ChicagoGetty Images

McDonald's is facing an unprecedented backlash from its workers over its stand on increasing the minimum wage. However, the firm's US ex-boss Ed Rensi, warned amid growing discord, that McDonald's may replace workers with robots, should the minimum wage be raised to $15 (£10) an hour.

Rensi served as the CEO of McDonald's US in the 1990s. He claimed that if the minimum wage rose to $15 an hour, it would "cause a job loss across this country like you're not going to believe". Despite reporting an increase in sales for three quarters in a row, McDonald's has been resistant to increasing the minimum wage.

"I was at the National Restaurant Show and if you look at the robotic devices that are coming into the restaurant industry -- it's cheaper to buy a $35,000 robotic arm than it is to hire an employee who's inefficient making $15 an hour bagging French fries -- it's nonsense and it's very destructive and it's inflationary and it's going to cause a job loss across this country like you're not going to believe," Rensi told Fox Business.

He added: "It's not just going to be in the fast food business. Franchising is the best business model in the United States. It's dependent on people that have low job skills that have to grow. Well if you can't get people a reasonable wage, you're going to get machines to do the work. It's just common sense. It's going to happen whether you like it or not. And the more you push this it's going to happen faster."

The Fight for $15 movement has focused most of its attention on organising protests targeting McDonald's. Although California and New York have already passed laws legalising the minimum wage to $15 an hour, members of the movement said they will continue to fight until all workers across the US earn $15 an hour as well, the Guardian reported.